The present invention relates to a method for the manufacture of structurally homogeneous flash-free lead battery terminals whereby the problems of battery failure due to electrolyte leakage from the battery either through the terminal itself due to cracks therein, or between the terminal and the battery case lid due to exterior terminal flashing which serves to function as a migratory leak channel through which the corrosive battery acid electrolyte can then escape, or battery leakage consequent from both such causes, are enabled to be substantially reduced or eliminated.
Lead is used as a battery terminal material for a number of reasons, among which are that it is a good electrical conductor, it is relatively cheap, generally corrosion resistant, and with proper precautions to avoid lead poisoning it is safe to handle. Lead is not, however, a particularly good material for use in a mechanical flexure-stress environment, and when a vibratory flexure-stress environment such as in a vehicular battery use application in an automobile or truck, boat, or airplane is combined with the corrosive battery acid electrolyte environment, lead battery terminals become more susceptible to mechanical failure.
Traditionally, lead battery terminals have been cast from the molten metal or alloys thereof, by methods and techniques long known and well established in the art. This method of lead battery terminal manufacture continues in widespread use, but produces a product which contains internal voids consequent from air entrainment during the casting process, as well as external seam flashing along the junctures of separable mold joining. In subsequent mechanical incorporation and use as battery terminal posts within the typical lead-acid storage battery cover or casing both the internal air pocket voids and the external seam flashing of the cast terminal, under the vibratory conditions in a typical vehicular use situation, when combined with the corrosive battery acid electrolyte environment, provide those defects known to be the most prevalent of causes in battery acid leakage due to terminal failure, either by way of vibratory corrosive cracking migration from the air entrained voids, or vibratory corrosive failure of the flashing web between the terminal-to-case joining.
A second way of manufacturing battery terminals is by the so-called cold forming method, where a cast lead billet or rod is cut to slug length and then fed to a hydraulic press where the terminal is formed in separable dies under pressure. This method does compact the lead to such an extent that all internal air pocket voids are eliminated, but under press pressure upon a slug within the separable forming dies, and with any appreciable die wear at all, an external flashing web will still be formed along the junctures of separable mold joining, with the subsequent problems attendant thereto as previously described with respect to battery terminal leakage failure of the flashing web between the terminal-to-case joining when subjected to a vibratory corrosive use environment.
With respect to both of the prior art methods of manufacturing lead battery terminals, whether by casting or cold forming, the cost of removing the external flashing web formed at the separable mold juncture lines when compared to the risks of subsequent battery leakage as is frequently consequent therefrom, in most use environments, is not considered to be either practical or economically feasible and lead battery terminals continue to be manufactured in one of the two foregoing ways.
In some liquid electrolyte battery applications, however, for example as is the case when such batteries are employed for back-up emergency power sources on nuclear submarines, and where the batteries are frequently positioned on their sides and located at remote and relatively inaccessible places within the ship, then any corrosive liquid leakage from such a battery would be unacceptable. In applications such as the foregoing, and in applications in general to provide battery terminals which do not have either the entrained air void or external flash defects, the present invention does provide a cost effective solution for overcoming these problems through a method of manufacturing structurally homogeneous flash-free lead battery terminals by the combined process of extrusion and automated machining. Although the mechanical elements of the present invention for accomplishment of the method herein taught are separately available as conventional machine centers for accomplishing various manufacturing operations, there is no known showing of the sequential combination of those particular machine elements or alternatives therefor, as herein taught, to provide both a new and novel result in the manufacture of structurally homogeneous flash-free lead battery terminals in the manner as hereinafter set forth.